Attempts to use photo-polymerizable compositions for the light-sensitive image forming layer of a light-sensitive planographic printing plate in the past have not been very successful. For example, a basic composition composed of a polymer as a binder, a monomer and a photo-polymerization initiator, as described in U.S. Pat. No. 3,458,311, a composition in which hardening efficiency is improved by introducing an unsaturated double bond into the polymer used as a binder, as described in U.S. Pat. No. 3,796,578, and compositions using a novel photo-polymerization initiator, as described in U.S. Pat. Nos. 3,549,367 and 3,751,259, and British Pat. No. 1388492 have been used. However, these light-sensitive compositions are disadvantageous in that their sensitivity is greatly influenced by the surface temperature of the light-sensitive planographic printing plate when imagewise exposing to light (hereinafter, this phenomenon is called temperature dependence). That is, the sensitivity under a condition at higher temperature, for example, in summer is sometimes 2 to 8 higher than that under a condition at lower temperature, for example, in winter.
As a result, when the optimum exposure of the light-sensitive planographic printing plate requires, for example, 10 seconds at a plate face temperature of 45.degree. C., satisfactory images can not be obtained by exposing to light at 10.degree. C. for 10 seconds, because 20-80 seconds are required at 10.degree. C. The operation is sometimes carried out early in the morning in winter at 10.degree. C. where there is the possibility that the temperature of the printing frame becomes more than 45.degree. C. when the operation is continuously carried out and the distance from the light source to the plate face is short. Thus, under such conditions, it is absolutely impossible to obtain stabilized images at the same exposure amount.
Further, these photo-polymerizable compositions are disadvantageous in that post-polymerization is caused after exposed to light by residual active seeds to increase the sensitivity with the passage of time before development (hereinafter, this phenomenon is called latent image sensitization).
In the photo-polymerizable compositions disclosed in the above cited patents, there is no exception and the latent image sensitization occurs, that is, the sensitivity after a long passage of time before development sometimes becomes 2 to 8 higher than that just after an exposure. Thus, accumulation of imagewise exposed light-sensitive printing plate is impossible in the plate making operation. This is a serious disadvantage of the light-sensitive planographic printing plates.
It has previously been found that the temperature dependence and the latent image sensitization can be reduced by using a light-polymerizable composition comprising
(A) a polymer having at least one group represented by the general formula (I) ##STR2## wherein R.sub.1 to R.sub.5 each represent a member selected from the group consisting of a hydrogen atom, halogen atom, a carboxyl group, a sulfo group, a nitro group, a cyano group, an amido group, an amino group and a substituted or unsubstituted alkyl group, aryl group, alkoxy group, aryloxy group, alkylamino group, arylamino group, alkylsulfonyl group and arylsulfonyl group and Z represents an oxygen atom, a sulfur atom, NH or NR, wherein R represents an alkyl group, and a carboxyl group on the side chain, PA0 (B) a monomer or oligomer having at least two polymerizable ethylenically unsaturated double bonds, and PA0 (C) a photo-polymerization initiator. PA0 (A) a polymer having at least one group represented by the general formula (I) ##STR3## wherein R.sub.1 to R.sub.5 each represent a member selected from the group consisting of a hydrogen atom, a halogen atom, a carboxyl group, a sulfo group, a nitro group, a cyano group, an amido group, an amino group and a substituted or unsubstituted alkyl group, aryl group, alkoxy group, aryloxy group, alkylamino group, arylamino group, alkylsulfonyl group and arylsulfonyl group, and Z represents an oxygen atom, a sulfur atom, NH or NR, wherein R represents an alkyl group; and a carboxyl group on the side chain, PA0 (B) a monomer or oligomer having at least two polymerizable ethylenically unsaturated double bonds, PA0 (C) a photo-polymerization initiator, and PA0 (D) a diazo resin. PA0 (A) a polymer having at least one group represented by the general formula (I) ##STR4## wherein R.sub.1 to R.sub.5 each represent a member selected from the group consisting of a hydrogen atom, a halogen atom, a carboxyl group, a sulfo group, a nitro group, a cyano group, an amido group, an amino group and a substituted or unsubstituted alkyl group, aryl group, alkoxy group, aryloxy group, alkylamino group, arylamino group, alkylsulfonyl group and arylsulfonyl group, and Z represents an oxygen atom, a sulfur atom, NH or NR, wherein R represents an alkyl group; and a carboxyl group on the side chain, PA0 (B) a monomer or oligomer having at least two polymerizable ethylenically unsaturated double bonds, and PA0 (C) a photo-polymerization initiator. PA0 (A) a polymer having at least one group represented by the general formula (I) ##STR5## wherein R.sub.1 to R.sub.5 each represent a member selected from the group consisting of a hydrogen atom, a halogen atom, a carboxyl group, a sulfo group, a nitro group, a cyano group, an amido group, an amino group and a substituted or unsubsituted alkyl group, aryl group, alkoxy group, aryloxy group, alkylamino group, arylamino group, alkylsulfonyl group and arylsulfonyl group, and Z represents an oxygen atom, a sulfur atom, NH or NR, wherein R represents an alkyl group; and a carboxyl group on the side chain, PA0 (B) a monomer or oligomer having at least two polymerizable ethylenically unsaturated double bonds, PA0 (C) a photo-polymerization initiator, and PA0 (D) a diazo resin.
It has now been found that improved sensitivity-stability in plate making operations, can be achieved when the above described photo-polymerizable composition is combined with a diazo resin.